JP2875669B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of controlling the output of a transfer charger to an appropriate value and improving transfer performance.

[0002]

2. Description of the Related Art The transfer performance of an image forming apparatus such as a copying machine is as follows.
It is determined mainly by the charge on the copy paper. Therefore, proper transfer performance can be maintained by detecting the charge on the copy sheet and inputting the detection information as feedback information to the power supply circuit (high-voltage DC power supply) of the transfer charger.

However, it is difficult to directly detect the charge on the copy sheet, and it is difficult to control the output of the transfer charger based on this detection information. For this reason, such a method has not been put to practical use at present.

Therefore, conventionally, a method of appropriately controlling the output of the transfer charger by detecting the charge on the photosensitive drum that has a correlation with the charge on the copy sheet has been performed. To explain a little more, the charge on the photoconductor drum at which transfer is performed properly is obtained by detecting the surface potential of the photoconductor drum with a surface potential detection sensor arranged around the photoconductor drum, The output circuit of the transfer charger is controlled by controlling the power supply circuit so that the surface potential of the drum becomes the determined surface potential.
More specifically, the output current to the transfer charger is controlled, and at the same time, constant current control is performed to keep the entire output current value constant at this time.

As another method, there is a method of performing constant voltage control instead of constant current control, or a method of performing a combination of both constant current control and constant voltage control.

Further, there has been a method in which an operator manually adjusts using a jig or a measuring instrument for adjustment without providing a surface potential detecting sensor. However, this method is time-consuming, and accurate adjustment cannot be performed. Therefore, at present, the above method is frequently used.

[0007]

However, since the above-described method is performed in a normal copying process, toner adheres to a wire or the like of the transfer charger, and the contamination of the transfer charger may change the impedance. . Therefore, accurate control could not be performed, and an appropriate transfer output could not be obtained. For this reason, it was difficult to stabilize the copy image quality in the above-mentioned conventional method.

Further, according to this method, it is necessary to arrange a surface potential detecting sensor and a signal line around the photosensitive drum, so that a necessary space must be secured around the photosensitive drum. As the configuration becomes larger and more complex,
There was a disadvantage that the cost was increased.

Further, there are disadvantages that the toner is wasted and the detection accuracy of the surface potential detecting sensor is deteriorated by other devices such as a charging charger.

The present invention has been made under such circumstances, and it is an object of the present invention to provide an image forming apparatus capable of solving the above-mentioned disadvantages of the prior art.

[0011]

According to the image forming apparatus of the present invention, the transfer charger and the discharge lamp are turned on each time a predetermined number of transfer operations are completed, and the detection of the drum current generated in the photosensitive drum is performed. Is performed for several seconds , a current detection circuit for detecting the average value, calculation means for calculating a difference between the average value of the current detection circuit and a preset reference value, and a difference calculated by the calculation means. Control means for outputting a control signal that can be eliminated to a power supply circuit of the transfer charger, thereby achieving the above object.

[0012]

The drum current is generated when the charge formed on the photosensitive drum by the transfer charger is removed by a discharging lamp. This drum current, more specifically, the current flowing through the drum tube of the photosensitive drum is 3, there is a proportional relationship with the surface potential of the photosensitive drum as shown in FIG. Also,
If the surface potential is known as described above, the charge on the photosensitive drum can be obtained. Therefore, if the drum current is detected, it is possible to know the charge on the photosensitive drum by the transfer charger.

Here, since the charge on the photosensitive drum has a correlation with the charge on the copy sheet that determines the transfer performance as described above, the output of the transfer charger is detected by using the detection signal of the drum current. Is controlled, the charge on the copy paper can be maintained at a desired value, and the copy image quality can be stabilized.

According to the present invention, the detection of the drum current by the current detection circuit is performed for several seconds each time a predetermined number of transfer operations are completed.
And the average value is detected. For this reason, the minute fluctuation of the drum current generated for several seconds does not adversely affect the detection accuracy. The calculating means calculates the difference between the average value and a preset reference value, and the control means outputs a control signal capable of eliminating the difference to the power supply circuit of the transfer charger, so that the output current value of the transfer charger can be controlled. Performed more accurately. Therefore, the copy image quality is stabilized.

In addition, this detection and control are performed during non-image formation in which toner is not supplied to the photosensitive drum.
Other devices such as charging chargers and image erasers are OF
Since it is set to F, the detection accuracy of the current detection circuit is not adversely affected. Further, the toner is not wasted.

[0016]

Embodiments of the present invention will be described below.

FIG. 1 shows the structure around the photosensitive drum of the image forming apparatus of the present invention. The configuration will be described below together with the operation during the copy process.

At a substantially central portion of the copying machine main body, a photosensitive drum 1 is provided.
Are provided rotatably in the direction of arrow A. The photosensitive drum 1 is manufactured by applying and forming a photosensitive layer on the surface of a drum tube made of aluminum. A flange 10 supported by an insulator is provided at both ends in the axial direction of the drum tube, and a shaft 1 serving as a rotation center of the drum tube and the photosensitive drum 1 is provided.
1 is electrically connected via a leaf spring (not shown). The shaft 11 is not directly connected to the copying machine main body grounded to GND (ground), but is grounded to GND via the current detection circuit 12.

Around the photosensitive drum 1, a charging charger 2, an inter-image eraser 3, a developing device 4, a transfer charger 5, a cleaning device 6, and a neutralizing lamp 7 are arranged from the upstream side in the rotation direction of the photosensitive drum 1. They are arranged in order. The charging charger 2 is exposed to light 8 from an optical system (not shown).
Prior to this, the surface of the photosensitive drum 1 is uniformly charged, and an electrostatic latent image is formed on the exposed portion.

After the inter-image eraser 3 erases the unnecessary image area, the developing device 4 supplies toner to the electrostatic latent image, and a toner image is formed on the photosensitive drum 1. This toner image is conveyed to the position of the transfer charger 5 as the photosensitive drum 1 rotates in the direction of arrow A. Transfer charger 5
, A predetermined DC current (transfer output current value) is supplied from the high-voltage transformer 50. This DC current is controlled in accordance with a control signal V _C input from the control circuit 51 to the high-voltage transformer 50, the details of which will be described later.

At the position of the transfer charger 5, a recording paper is conveyed from a paper feeding unit (not shown) via a registration roller 9 in synchronization with the rotation of the photosensitive drum 1, and the photosensitive drum 1 is transferred to the recording paper. The upper toner image is transferred. The recording paper onto which the toner image has been transferred is conveyed by a conveying belt 20 to a position of a fixing device (not shown), where a fixing process of the toner image is performed. The recording paper on which the toner image has been fixed is then discharged outside the apparatus.

On the other hand, on the surface of the photoreceptor drum 1 after the transfer, a part of the toner not contributing to the transfer remains as waste toner, and there is a residual charge. The waste toner is scraped off by the cleaning blade 60 of the cleaning device 6. Further, the residual charges are eliminated by the neutralization lamp 7.

In addition to the above-described copying process, the copying machine generates the photosensitive drum 1 in a non-copying process.
More specifically, a detection process is provided for detecting the drum current _ID flowing through the drum tube and controlling the output current value of the transfer charger 4 according to the detection result.

FIG. 2 shows the operating state of each device in this detection process. As shown in FIGS. 2A and 2C, in the detection process, unlike the copy process described above, the photosensitive drum 1 is used. Of the devices excluded, only the transfer charger 5 and the neutralizing lamp 7 are turned on, and the other devices are in the off state ((b), (f), (g) in FIG.
(H)).

However, as shown in FIG. 1E, the magnet roller 40 of the developing device 4 is rotated idly of the photosensitive drum 1 in order to prevent unnecessary toner from adhering to the photosensitive drum 1. A _DY bias similar to that at the time is applied. Therefore, toner is not wasted when the detection process is performed.

In this detection process, when the transfer charger 5 is turned on, negatively charged charges are generated on the photosensitive drum 1, more specifically, on the drum tube as shown in FIG. The charged charges are conveyed to a position facing the neutralizing lamp 7 with the rotation of the photosensitive drum 1 and are neutralized by the neutralizing lamp 7. At this time, a drum current _ID [μA] is generated in the drum tube.

As shown in FIG. 3, the drum current _ID is proportional to the surface potential [V] of the photosensitive drum 1. Further, if the surface potential is known as described above, the charge of the photosensitive drum 1 can be obtained. Therefore, the drum current I
_{If D} is detected, it is possible to determine the charge charged on the photosensitive drum 1 by the transfer charger 5.

Therefore, in the present invention, the drum current _ID is detected by the current detection circuit 12 connected to the shaft 11 of the photosensitive drum 1. The current detection circuit 12 detects the drum current I _D
When detecting, it is converted into a voltage signal V _D, and outputs it to the control circuit 51 to be mounted to the copying machine main body.

The control circuit 51 is to be a control center of the copying machine, the current A / D converter to read when needed voltage signal V _D from the detection circuit 12, the voltage read by the A / D converter comprising a RAM and a CPU or the like that temporarily stores and holds the signal V _D. Control circuit 5
1, more specifically CPU, it calculates the difference between the preset reference voltage signal and the voltage signal V _D, the control signal (control voltage signal) V _C to the high voltage transformer 50 as a feedback signal by the calculation result Output.

More specifically, the reference voltage signal has a correlation with the charge of the copy paper, and is a value corresponding to the charge of the photosensitive drum 1 which can obtain a preferable copy image quality. Voltage signal V _D for the signal
Is calculated, and the calculated deviation value is temporarily stored in the RAM.
Then, when the copy process is restarted, R
The operation deviation value stored in the AM is read, and a control signal V _C capable of eliminating the operation deviation value is supplied to the high-voltage transformer 50. Thereby, in the copy process, the output current value of the transfer charger 5 (transfer total current value) I _T [μ
A] is always controlled to a value at which an appropriate copy image quality can be obtained. Incidentally, high-voltage transformer 50 by constant current control, providing an output current value I _T corresponding to the control signal V _C to the transfer charger 5.

[0031] As described above, in the present invention, provided the detection process in addition to the copy process, detects the drum current I _D only during the detection process, controls the output current value I _T of the transfer charger 5 by the detection signal With such a configuration, adverse effects on the detection accuracy by other devices such as the charger 2 can be reliably eliminated. Therefore,
Accurate detection becomes possible. Although the drum current _ID is also generated in the copy process, the CPU does not read the detection signal from the current detection circuit 12 during this time.

FIG. 4 shows the transfer total current value _IT [μ] on the vertical axis.
A] shows the relationship between the detection process and the copy process with the number of copies taken on the horizontal axis. As can be seen from the figure, this detection process is performed at the time of warm-up of the copying machine or every time a predetermined number of copies are made. During the detection and the copying process, the transfer total current value _IT is kept constant.

As shown in FIG. 4, the detection of the drum current _ID may be performed for several seconds. In other words, if the measurement is performed for several seconds and the average value is obtained, adverse effects on the detection accuracy due to the minute fluctuation can be reliably prevented, and the output current value of the transfer charger 5 can be controlled more accurately.

According to the above embodiment, unlike the conventional example,
Since there is no need to provide a surface potential detection sensor around the photosensitive drum 1, space saving around the photosensitive drum 1 can be achieved, which can greatly contribute to downsizing of the apparatus configuration and cost reduction. Also, in the detection process, the static elimination lamps 7 to
Since the charge between the transfer chargers 5 is removed by the charge removing lamp 7, the toner is not wasted. Therefore, the running cost can be reduced.

Further, since the charge on the photosensitive drum 1 does not change even after passing through the position of the cleaning device 6, there is no need to provide a contacting / separating moving mechanism or the like on the cleaning blade 60 for the detection process. As described above, the present invention can be implemented by utilizing the existing configuration of the copying machine, and therefore has the advantage that there is no need to change the design.

In the above embodiment, the case where the present invention is applied to a copying machine has been described. However, the present invention can be similarly applied to other image forming apparatuses such as a printer.

[0037]

According to the above-described image forming apparatus of the present invention, in the detection process, the detection of the drum current is performed by the current detection circuit for several seconds each time a predetermined number of transfer operations are completed. , Detect the average value, so the drum current for a few seconds
The minute fluctuation occurring during the period does not adversely affect the detection accuracy. The calculating means calculates the difference between the average value and a preset reference value, and the control means outputs a control signal capable of eliminating the difference to the power supply circuit of the transfer charger.
Since the control of the output current value of the transfer charger is performed with higher accuracy, the first advantage is that the copy image quality can be stabilized.

Secondly, unlike the conventional example, there is no need to provide a surface potential detection sensor around the photosensitive drum.
There is an advantage that the space around the photosensitive drum can be saved, which can greatly contribute to downsizing of the device configuration and cost reduction.

Third, in the detection process, the photosensitive drum is discharged by the discharge lamp, so that there is an advantage that the toner is not wasted and the running cost can be reduced.

Fourth, in the detection process, since other devices such as the charging charger are turned off, there is an advantage that the drum current can be detected with high accuracy, and as a result, the output of the transfer charger can be controlled with high accuracy.

Fifth, since the output of the transfer charger is automatically controlled, the adjustment operation can be performed quickly and reliably.
There is also an advantage that serviceability can be improved.

[Brief description of the drawings]

FIG. 1 is a front view showing a configuration around a photosensitive drum of a copying machine to which the present invention is applied.

FIG. 2 is a graph showing a relationship between a surface potential of a photosensitive drum and a drum current.

FIG. 3 is a graph showing a relationship between the number of copies and a total transfer current.

FIG. 4 is a timing chart showing operation timing in a detection process.

[Explanation of symbols]

1 photoconductive drum 5 the transfer charger 7 discharging lamp 12 current sensing circuit 50 high-voltage transformer 51 control circuit I _D drum current V _D voltage signal V _C control signal I _T transfer charger output current value

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/16

Claims (1)

(57) [Claims] 1. A transfer charger and a discharge lamp are turned on each time a predetermined number of transfer operations are completed, and detection of a drum current generated in a photosensitive drum is performed for several seconds. A current detecting circuit for detecting a value of the current detecting circuit; a calculating means for calculating a difference between the average value of the current detecting circuit and a preset reference value; and a control signal for eliminating the difference calculated by the calculating means. an image forming apparatus including a control means for outputting to the power supply circuit of the charger, the.